While I am continuing my practice with the German drawings of the V2 rocket, I have come across the PG designation a couple of times on different drawings. I originally thought it was for diameter, but its not lining up with some of the other dimensions in the drawing.
In the following drawing PG 21 appears to be dimensioning the the outside of the threads. however the hole through the bushing is is dimensioned at 21 as well. There is no physical way they can both be 21.
In the example below the PG 21 notation is used for both male and female threads and they do appear to line up. However there seems to be more than a 1 mm difference between the interior 20 mm hole and the threads.
What does the PG notation mean?